How do I segment each part of a DICOM image?
I looked at some picture from DICOM, and it seems that these images usually don't have many local minima, so I guess that's why watershed isn't optimal.
However, it seems that in DICOM the color gradients are often strong, so I suggest to use techniques that works well with gradients:


Direct Gradient computations, either convolutional gradients or morphological gradients (selects shape of your different objects)
Normalized Cut on Similarity Graphs


If you want to know more about these you can read this post.